Audio fetal stimulators are commonly used in clinics to evaluate both the general health and hearing of fetuses in utero. Audio stimulation devices can include both artificial larynxes and devices which employ speakers to “communicate” with the fetus, such as those described in U.S. Pat. Nos. 6,169,814 and 5,913,834. In each of these devices, an audio sound source is generated externally and is transmitted into the abdominal cavity of the mother to stimulate the fetus. Movement of the fetus can be monitored to track reaction to the audio stimulation, and therefore to verify general hearing, assess fetal health based on response to the stimulation, and to analyze other parameters.
While these audio stimulation devices are useful for general testing of both the overall hearing and response of the fetus, there are certain limitations associated with audio stimulation devices of the type described above. These devices, for example, produce sound which is transmitted to the abdominal cavity with little or no directivity. Because the audible sound has very long wavelengths, it tends to spread equally in all directions in the abdomen. Therefore, when audio stimulation is applied to test hearing, the sound is transmitted simultaneously to both fetal ears. It is not possible to test each of the ears individually. Furthermore, although the sound stimulation causes the fetus to move, prior art methods are not designed to cause the fetus to move to a particular position or location in the uterus. Because the sound is almost non-directional, there is no “quiet” place in the uterus at which the fetus would feel less stressed. Hence the fetus moves almost randomly to the audio stimulation.